In order to convey, for example, works in the form of a thin plate, there have heretofore been used suction pads connected to a vacuum and suction source. A suction pad of this kind generally comprises a root part and a skirt part integrally joined thereto, is installed on an arm of a robot through a fitting and is utilized for the conveyance of works or the like.
At that time, a tube from the vacuum and suction source is connected to the root part of the suction pad to suck air from the interior of the suction pad, whereby the work is held by the suction pad under a pressure reducing action of the skirt part.
Operation of a suction pad according to such prior art will hereinafter be described with reference to FIG. 1.
Reference character 2 designates a suction pad. The section pad 2 comprises a cylindrical root part 4 connected to a vacuum and suction source (not illustrated) and a skirt part 6 integrally joined to the root part 4.
When a work 8 is to be conveyed, the suction pad 2 is installed on an arm of a robot (not illustrated) so as to displace the suction pad 2 by the robot, thereby bringing the peripheral edge of the skirt part 6 into close contact with the work 8. A vacuum and suction source (not illustrated) is then operated to reduce the pressure within the suction pad 2, whereby the suction pad 2 holds the work by suction and then conveys the same.
However, a fitting to be connected to the suction pad 2 is generally rotatably inserted in a hole defined in the root part 4 of the suction pad 2 to connect them to each other. Therefore, angular moment generates about an axis of the suction pad 2 as the robot arm (not illustrated) angularly moves upon the conveyance of the work 8. Accordingly, the suction pad 2 rotates and hence, the work 8 held to the suction pad 2 also rotates, so that exact positioning of the work 8 becomes difficult. In particular, when a work 8 having a particular shape is conveyed and then intended to position on a predetermined site, as described below, this positioning becomes substantially difficult if the suction pad rotates.
As a method of preventing the angular movement of the suction pad 2, it is considered to fixedly attach the fitting, for example, by coating and baking an adhesive. However, this method causes the following inconvenience. Namely, when the exchange of the suction pad 2 is attempted according to the kind, size, etc. of the work, it is often required to exchange the fitting fixed to the suction pad 2, also. Therefore, it is substantially impossible to exchange the suction pad 2 alone.
For this reason, fittings must be always provided according to the number of suction pads. There are also pointed out disadvantages of increase in the number of spare parts, complicated inventory control, etc.
In addition, there is a problem that although the skirt part 6 of the suction pad 2 is somewhat flexible, the suction pad 2 does not come into close contact with the work 2 as illustrated in FIG. 1 if the work 2 has a rough surface. Therefore, the pressure within the suction pad 2 can not be reduced even under the pressure reducing action by the vacuum and suction source, so that sufficient suction force can not be provided.
Accordingly, a mold has been fabricated in such a manner that the skirt part 6 conforms to the shape of the work 8 to cope with such a problem. However, such a measure causes an inconvenience of requiring many steps.